Photolabile protecting groups (PLPG) play an important role in blocking functional groups present in nucleosides, nucleotides, sugars and amino acids, which are used for the synthesis of biomolecules, e.g. nucleic acids and their derivatives, proteins, peptides and carbohydrates. Additionally, PLPG have the advantage that deprotection of the protected functional group can be performed simply via light exposure. Therefore, PLPG provide the basis for the photolithography based spatially resolved synthesis of oligonucleotides or peptides on solid supports. The major advantage of this technique is that high resolution microarrays can be produced. Such high resolution microarrays are of great significance for the analysis of biomolecules in medicine and pharmaceutical research, as they provide the possibility to perform high throughput and cost-effective analysis of multiple samples on a single array. Examples of PLPG used for oligonucleotide synthesis include, but are not limited to, α-methyl-6-nitropiperonyl-oxycarbonyl (MeNPOC), and 2-(2-nitrophenyl)-propoxycarbonyl (NPPOC). Examples of PLPG used for photolithography based peptide synthesis are for example nitroveratryloxycarbonyl (NVOC) and 2-nitrobenzyloxycarbonyl (NBOC).
Previous PLPG synthesis used light at a wavelength of approximately 365 nm or shorter for the deprotection of the protected functional groups. Light sources which are suitable to generate such wavelength, are e.g. mercury arc lamps, excimer lasers, UV-LEDs and frequency multiplied solid-state lasers. Such light sources are characterized by high purchase costs, provide limited luminous power and have a short life-time leading to high overall costs of operation. Since some of the above mentioned light sources contain hazardous substances, e.g. mercury, and appropriate actions to secure occupational safety and proper disposal are necessary, further increasing the costs.
Optical devices used for the photolithography based synthesis of oligonucleotides or peptides, such as micro mirror devices (WO 03/065038), are primarily designed for the visible wavelength range of approximately 380 to 780 nm. Such devices carry an antireflective or protective antiscratch coating optimized for transparency for the respective visible wavelength range. Thus, the near UV wavelength of 365 nm used for the deprotection of the functional groups protected with PLPG require optical devices which are optimized for near UV wavelengths. Since most of the optical devices are optimized for the use with visible light, such optimization often comprises removing the coating intended for the use with visible light from the optical devices and/or coating the optical device with materials intended for use with near UV or UV light.
Furthermore, many light sources produce a broad spectrum of wavelengths from the UV- to the IR-range, both of which have disadvantageous effects concerning the synthesis of biomolecules. As a result DNA or peptide microarrays might be of low quality due to undefined lengths of the synthesized DNA strands and peptides, respectively.